Sometimes you'll know an address that you would like to block from having any access at all to your server. You can do that by creating
the rc.firewall.blocked file under /etc/rc.d/ directory and uncomment the following
lines in your firewall rules scripts file:

Create the rc.firewall.blocked file touch /etc/rc.d/rc.firewall.blocked and add inside this file all the IP addresses that you want to block from having any access to your
server at all:
For example, I put the following IP addresses in this file:

Example 12-1. rc.firewall.blocked

204.254.45.9
187.231.11.5

Further documentation, more details, there are several man pages you can read: